The present invention relates to a drive for a grinding wheel of a cam grinding machine with which cams having concave flanks can be ground out.
The grinding of cams having concave contours belongs to the prior art, in which case grinding wheels whose radius is smaller than a radius of curvature of a concave region of the cams are used. DE 44 26 452C1 discloses, inter alia, a machine for grinding cams, having concave flanks, of a camshaft which uses three grinding wheels. The machine comprises a slide which is traversable on a bed of the machine in a radial direction relative to the camshaft to be ground and on which two grinding spindles having a rough-grinding wheel and a finish-grinding wheel are mounted. The two grinding spindles are mounted in a common spindle head in such a way that the spindle axes intersect at an angle or run parallel to one another. The spindle head is pivotable about an axis running perpendicularly to the camshaft. A third grinding wheel, the diameter of which corresponds to approximately twice the radius of the concave flanks of the cams to be ground on the camshaft, is arranged next to the finish-grinding wheel on its grinding spindle. This prior art does not contain any more detailed information on the type of drive of the grinding spindles.
A grinding machine which is constructed according to the piggyback principle has previously been described in DE 41 37 924 C2. This machine comprises a first grinding slide, which is movable in a direction perpendicular to a longitudinal axis of the camshaft and carries a first grinding wheel having a large diameter. Arranged on the first grinding slide is a second grinding slide having a second grinding wheel, which has a smaller diameter than the radius of curvature of the cam flank, to be ground out, of a cam. This prior art also does not contain more extensive information on the drive of the grinding spindle.
DE 196 35 687 discloses a camshaft grinding machine in which the grinding spindle unit is mounted hydrodynamically or hydrostatically.
Finally, grinding machines whose grinding spindles have either a direct drive via a high-frequency grinding spindle motor or a belt drive belong to the prior art. However, the grinding spindles driven directly with a high-frequency motor have the disadvantage that the high-frequency motors, on account of their size, permit only limited dimensions of the camshafts with regard to their length and of the cam pitch with regard to the base circle radius. On the other hand, the grinding spindles driven with a belt drive have the disadvantage that only limited outputs at predetermined belt pulley diameters can be transmitted, and the belt, which is necessarily present, when deflected at right angles, applies high radial forces to an adjacent bearing on account of its pretension.
The object of the present invention is to provide a drive for a grinding wheel, with which drive the disadvantages of a direct drive using a high-frequency motor and of a drive using a belt drive are removed. In addition, the drive is to be capable of being produced in different diameter ratios and lengths, so that outputs and speeds can be transmitted within wide ranges.
The above object is achieved according to the present invention in such a way that a drive of a grinding spindle unit for transmitting the output and the torque of a grinding spindle motor is effected magnetically. Provided for this purpose is a drive wheel which is connected to a drive motor. Arranged on the circumference of the drive wheel are equispaced permanent-magnet rings, and meshing in clearances between the latter are permanent-magnet rings which are arranged in an equispaced manner on grinding spindle rotor. The permanent-magnet rings of the drive wheel and of the grinding spindle rotor are arranged relative to one another in a non-contacting manner. An air gap provided in each case in the axial direction is, for example, 0.05 to 0.4 mm. In this case, the magnet rings arranged on the drive wheel engage in the spaces formed by the equispaced magnet rings of the grinding spindle rotor, and vice versa.
In an embodiment of the present invention, a circumferential width of the drive wheel has equispaced recesses which are arranged in a radially encircling manner and which are lined at their flat sides with small permanent magnets. With due regard to the width of the recesses, lined with permanent magnets of the drive wheel, recesses fitting into these clearances are provided on a circumferential width of the grinding spindle rotor and are likewise lined laterally at the flat sides with permanent magnets. This design also takes into account the fact that the annular flat sides, lined with permanent magnets, of the recesses do not touch one another during the torque transmission, i.e., they are at a distance from one another. In this design, too, the air gap in the axial direction is, for example, 0.05 to 0.4 mm.
The center axes of the drive motor and the drive wheel are in alignment with one another and are arranged parallel to the center axis of the grinding spindle rotor. The center axis of the grinding spindle rotor is in turn preferably arranged in a horizontal and vertical plane parallel to the center axis of the camshaft.
The drive motor with drive wheel and the grinding spindle rotor are each arranged in a housing, and these housings are connected to one another by means of screws. These two housings connected to one another are fastened to a grinding spindle-head housing traversable in the X-axis direction. The grinding wheel is located on one free end of the grinding spindle rotor. The two end regions of the grinding spindle rotor are mounted in rolling bearing assemblies preloaded without play, the grinding-wheel-side end of the grinding spindle rotor serving as a fixed bearing unit and the opposite end serving as a floating bearing unit.
The complete grinding spindle unit comprises a housing which is of thin-walled design, so that there is still sufficient space relative to adjacent cams of a camshaft; for the cams arranged next to each other on the camshaft, on account of different angular positions of the cams on the camshaft, have a radius of revolution which is enlarged relative to the cam-base radius.
The complete grinding spindle unit housed towards the camshaft and fastened to the housing can be completely replaced by other grinding spindle units. In this way, it is possible for grinding spindle units of different size, i.e., size graduation, to be used for different applications, since no supply lines lead to the bearings and to the grinding spindle unit. This provides the advantage that, for different applications during grinding, in particular with regard to the grinding wheel diameter, different grinding spindle units can be changed over by simple replacement. Depending on the grinding problem to be solved on the spot, the respectively suitable grinding spindle unit can therefore be used, the ratio of the diameters of the drive wheel and of the grinding spindle rotor determining the transmission ratio. If the diameter of the grinding spindle rotor is enlarged, the torque which can be transmitted is increased, for a larger torque must be available during the use of larger grinding wheels.
The above drive according is characterized in that the drive motor and the drive wheel have a housing, in that the housing, in the region of the arrangement of the grinding spindle rotor, has an opening corresponding to the grinding spindle length and the diameter, in that the grinding spindle, in that the grinding spindle rotor has a sectional housing, in that the grinding spindle rotor is mounted at each end in the sectional housing, and in that the sectional housing can be mounted in a suitably interchangeable manner on the opening of the drive housing. Furthermore, the grinding spindle rotor has a spindle nose, on which a grinding wheel can be fastened by means of a fastening element.